Hess's Law

The standard enthalpy change for the combustion of graphite is −393.5 kJ/mol and that of diamond is −395.4 kJ/mol.

What is the enthalpy change for the reaction below, in kJ/mol?

C _{(s, graphite)} → C _{(s, diamond)}

• −1.9

• +1.9

• −788.9

• +788.9

Calculate the change in Enthalpy of the combustion reaction of liquid Ethanol (C2H5OH). When Ethanol has an enthalpy of -286 kJ/ mol, water is liquid and oxygen and carbon dioxide are in gas state.

• -286 kJ/ mol

• 1366 kJ/mol

• -2732 kJ/ mol

• -1366 kJ/mol

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

The standard enthalpy changes of formation of carbon dioxide and of methanoic acid are −394 kJ/mol and −409 kJ/mol respectively. Calculate the enthalpy change for the reaction

H_{2 (g)} + CO_{2 (g)} → HCOOH _(l)

• −803 kJ/mol

• −15 kJ/mol

• +803 kJ/mol

• +15 kJ/mol

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

 How many joules of heat are needed to raise the temperature of 10.0 g of aluminum from 22°C to 55°C, if the specific heat of aluminum is 0.90 J/gx°C?    

• 297 Joules
• 0.003 Joules
• 297 J/gx°C
• 0.003 J/gx°C

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

The enthalpy change for the reaction
C(s, graphite) + 1⁄2O₂(g) --> CO(g) cannot be measured directly since some carbon dioxide is always formed in the reaction.
It can be calculated using Hess’s Law and the enthalpy changes of combustion of graphite and of carbon monoxide.
C(s, graphite) + O₂(g) --> CO₂    ΔH=-394 kJmol^–1
CO(g) + 1⁄2O₂(g) --> CO₂  ΔH=-283 kJmol^–1  
The enthalpy change for the reaction of graphite with oxygen to give carbon monoxide is 

• -677 kJmol^–1 
• +111 kJmol^–1 
• -111 kJmol^–1 
• +677 kJmol^–1 

The enthalpies of combustion of C(s), H2(g) and C4H9OH(l) (in kJmol^-1) are as follows  
C(s) + O₂(g)   ->  CO₂(g)                                               ∆H=a
H₂(g) + ½O₂(g)   ->   H₂O(l)                                        ∆H=b
C₄H₉OH(l) + 6O₂(g)   ->   4CO₂(g) + 5H₂O(l)  ∆H=c
What is the enthalpy change for the reaction shown below?
  4C(g) + 5H₂(l) + ½O₂(g)   ->   C₄H₉OH(l)

• c – 4a – 5b
• 2a + 10b - c
• 4a + 5b - c
• 2a + 5b + c

Tags

NGSS.HS-PS1-4

The standard enthalpy changes of combustion of carbon, hydrogen and methane are shown in the table. 
Which one of the following expressions gives the correct value for the standard enthalpy change of formation of methane in kJ mol^–1?
C(s) + 2H₂(g) → CH₄(g) 

• 394 + (2 × 286) – 891 
• –394 – (2 × 286) + 891 
• 394 + 286 – 891 
• –394 – 286 + 891 

Tags

NGSS.HS-PS1-2

NGSS.HS-PS1-4

Given the following data: ΔH^○_f[FeO(s)] = –270kJmol^–1
ΔH^○_f [Fe₂O₃(s)] = –820 kJ mol^–1
Select the expression which gives the enthalpy change, in kJ mol^–1, for the reaction:
2FeO(s) + 1⁄2O₂(g) → Fe₂O₃(s) 

• (–820 × 1⁄2) + 270 = –140
• (+820 × 1⁄2) – 270 = +140
• –820 + (270 × 2) = –280 
• +820 – (270 × 2) = +280 

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

C₂H₄(g) + H₂(g)   ->   C₂H₆(g)  ∆H°=-137 kJ mol^-1
Which statement about this information is correct?

• The total energy of the bonds broken in the reactants is greater 
  than the total energy of the bonds 
  formed in the product 
• The bonds broken and the bonds made are of the same strength 
• The total energy of the bonds broken in the reactants is less than the total energy of the bonds formed in the product 
• No conclusion can be made about the sums of the bond enthalpies in the product compared with the reactants 

Tags

NGSS.HS-PS1-4

Use the chart to answer the following question.
Which is correct about energy changes during bond breaking and bond formation? 

• A
• B
• C
• D

Tags

NGSS.HS-PS1-4